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ER40 collet chuck

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dtsh

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#1
I had made mention a few months back that I was working on making an ER40 collect chuck for the spindle of my lathe. I finished it tonight; however, I am unsatisfied with the result and will make a second attempt at making a better one.

The main reason I think it's a failure was that I managed to cut the internal threads for the spindle a bit too large, leaving more slop in the threads than I'm comfortable with. I've not made many projects on a lathe since high school. It's not a complete failure as I've certainly gained some knowledge and I suspect I can salvage it as a hex collect block.

The bar is oddly shaped, mostly round'ish with some flat spots. Imagine half a hex bar joined to half a round bar, but kinda lopsided and you're close to the shape. The 3 jaw chuck is too small to hold the piece, so I center drilled it for an arbor. I superglued the arbor in place, chucked it up and started working on it.

It was, for the most part, pretty straight forward. I bored out one end to fit the spindle, using a plug guage I'd prepared earlier for comparison. Cutting internal threads was a first for me and while the threadform came out fine, I overshot the maximum for 1 7/16-12 and ended up producing a loose fitting part. I had considered boring it out and sleeving it, but it would have made for thinner walls in a press-fit part than I felt comfortable attempting, so I pressed on knowing that this was now just a dress rehearsal and I'd have to start all over.

I set my compund to cut an 8 degree taper and mounted the collect chuck to the spindle and bored out the other end to accept an ER40 collet. As I closed in on the final size, I checked the fit of a collet and decided to adjust my compound slightly to make a nice fit.

It was also the first time cutting metric threads, M50 x 1.5, so I wasn't sure what to expect. I wrote a ruby script to calculate change gears and settled on 78t, 30t/18t, 66t as the best match, yielding a pitch of roughly 1.501 - close enough. The calculated change gears produced a thread that matches the nut quite well. I was very happy with that part of it.

er40_spindle1.jpg

er40_spindle2.jpg

er40_spindle3.jpg


Now I've got to try this again, this time with a little more experience. The issue with the spindle threads aside, I think it turned out well.

I had repeated issues with chatter, which I think was from my HSS bits being improperly ground.
 
Last edited:

warrjon

Swarf
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Jun 26, 2018
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#2
Good job, I like ER collets as they have a wide holding range.
 

Tozguy

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#3
I'd say that for a first try that you did real good. I made three ER chucks before getting it right.
Allow me to offer a reminder that spindle threads need to be free enough to allow the chuck to register properly on the shoulder of the spindle.
 

dtsh

H-M Supporter - Sustaining Member
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#4
I'd say that for a first try that you did real good. I made three ER chucks before getting it right.
Allow me to offer a reminder that spindle threads need to be free enough to allow the chuck to register properly on the shoulder of the spindle.
Thanks fo the reminder, I certainly had them free enough. I doubt there was much contact as until snugged up on the shoulder there was significant play, but I'll keep that in mind for the next try.
 

dtsh

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#5
Worked on this a little, drilled it for an arbor and started getting it from "roundish" to round again. Mostly just focusing on being able to get the steady rest
in there for drilling/boring.

Here's the raw bar
er40_2_001.jpg

and where I ended up stopping for the day.
er40_2_002.jpg

Slow going with the interrupted cut, I managed to slip the belt a few times.
 

Bob Korves

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#6
Spring passes are what get you with internal turning and threading. There is a lot of flex in those bars. When you get roughly close to final dimension, take enough passes for the tool to quit cutting, see what you have, and then proceed slowly, allowing the tool to reach the depth of cut with the spring out. Dull tools make it even more difficult. Import brazed carbide boring bars are also often poorly ground, and rub on the work below the cutting edges. Look for rubbing, you can try Sharpie marks to help find the rubbing. Make sure the tool is sharp and the cutting edge is on center line. If necessary, you can twist the tool down so it is cutting at a negative rake, which gives more clearance on the relief surfaces, helps to stop chatter, and cuts way better than you might imagine (use this only on turning, not threading, unless you regrind the tool, because it will change the thread angle.) If you twist the tool, you must also change the tool height.

Boring bars and similar internal threading tools cause lots of problems with oversize holes and threads due to spring in the tools. Beware of it and pay attention as you get to the final cuts. Solid carbide tools help a lot, but are $$.
 
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